textproduct: Rapid City

KEY MESSAGES

- Upper ridge will dominate the weather through early next week.

- Isolated severe thunderstorms may occur late this afternoon/evening in/near the Black Hills to SD/NE border

- Isolated severe thunderstorms may occur over northeastern WY late Saturday

- Temperatures will average about 4-8F above normal.

DISCUSSION

(This Afternoon Through Thursday) Issued at 1149 AM MDT Fri Aug 21 2026

Current upper-air analysis and water vapor imagery depict large- scale ridging continuing to strengthen over the southwest. Satellite imagery indicates partly cloudy skies behind the thunderstorms and showers that moved through the region this morning. Current radar scans show a few weak returns associated with showers/virga over western SD. Surface observations show temperatures mainly in the 80s, with dewpoints in the 40s across northeast WY transitioning to the low 60s across south-central SD. Winds are generally easterly across western SD and southerly across northeast WY at 10 to 17kts, gusting to 25kts. Campbell Co. in particular may see gusty northeasterly winds up to 25kts, behind a weak frontal passage, and minRH values in the upper teens this afternoon. Due to these conditions, elevated fire weather concerns will continue to persist through this afternoon for Campbell Co.

There is still uncertainty around today's chances for thunderstorms across southwestern SD, both in timing and severity, with disagreement remaining among the CAMs. However, MLCAPE values of ~750-1250 J/kg, dewpoints in the 50s to low 60s in the SD plains, and 0-6km bulk wind shear values around 55kts indicate that the environment in southwestern SD could support thunderstorm development and a supercell or two. The timing of the shortwave today, the cap currently in place, and the strong vertical moisture gradient between the SD plains and the Black Hills will all play a large role in storm development this afternoon/evening and into the overnight hours.

Due to these factors, there is a slight risk for severe thunderstorms southeast of Rapid City down to the SD/NE border, with the primary threats being large hail (up to 2") and damaging winds (60-70+ mph). As a result, 15 percent POPs were added to the southern Black Hills and into southwestern SD for this afternoon into the evening.

Multiple disturbances riding along the ridge will keep scattered thunderstorms chances in play for Saturday and Sunday, with northeast WY favored for better coverage Saturday. As is typical for thunderstorms in August, chances for precipitation will be hit-and- miss. Cloud cover and storm placement will also drive day-to-day temperatures, though highs are expected to remain above average across most of the region through the weekend and into next week as the ridge remains in place.

AVIATION

(For the 18Z TAFS Through 18Z Saturday) Issued At 1113 AM MDT Fri Aug 21 2026

Isolated thunderstorms may occur later this afternoon near the Black Hills and then toward the SD/NE border after 22/00z. Any storm may contain local IFR conditions as well as hail/strong gusty erratic winds. Outside of thunderstorms, VFR conditions will prevail.

FIRE WEATHER

Issued At 1149 AM MDT Fri Aug 21 2026

Elevated fire weather concerns will continue through this afternoon for Campbell Co., where gusty northeasterly winds up to 25kts will combine with minimum relative humidity values in the upper teens. Thunderstorm chances increase across northeast Wyoming late Saturday afternoon, increasing the dry lightning risk, however, relative humidity values will increase to the upper 30s to low 40s.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.